> The second is the Apple style on-device CSAM scanner?

This is exactly what has been proposed. E.g. WhatsApp has a piece of code that scans images and texts before sending. After that, they are "encrypted".

This is of course a massive privacy violation, since the code that scans for CSAM can be switched out to scan for anything else at any time. (It's even easier to do now than when Apple first proposed it, as language models since have gotten good at reading images.)